Note: Descriptions are shown in the official language in which they were submitted.
CA 02496922 2011-03-25
Silanised, Structurally Modified, Pyrogenically Produced
Silica
The invention relates to a silanised, structurally
modified, pyrogenically produced silica, a process for the
production thereof and its use.
It is known to use nanoscale particles in transparent
coating compositions.
Thus, according to US 6,020,419, pyrogenically produced
silicon dioxides, deagglomerated in situ, which have been
made hydrophobic with dimethyldichlorosilane (Aerosilo R
972), are used in polyurethane lacquers to improve the
scratch resistance of the coatings.
The known silica has the disadvantage that it cannot be
produced in powder form without a lacquer binder.
The object therefore existed of developing a silica that
does not have these disadvantages.
The present invention provides silanised, structurally
modified, pyrogenically produced silicas, which are
characterised by groups fixed on the surface, the groups
being dimethylsilyl and/or monomethylsilyl, preferably
dimethylsilyl.
In a preferred embodiment of the invention the silicas can
have the following physico-chemical characteristics:
BET surface area m2/g: 25 - 400
Average size of the primary particles nm: 5 - 50
pH value: 3 - 10
Carbon content 0.1 - 10
DBP value < 200
The silica according to the invention can have a tamped
density of 100 to 280, preferably 100 to 240 g/l.
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A tamped density of more than 280 g/l leads to poorer
results in the technical lacquer tests.
Pyrogenic silicas are known from Winnacker-Kiichler
Chemische Technologie, volume 3 (1983)
4th edition, page 77 and
Ullmanns Enzyklopadie der technischen Chemie, 4th edition
(1982), volume 21, page 462.
In particular, pyrogenic silicas are produced by flame
hydrolysis of vaporisable silicon compounds, such as e.g.
SiC14, or organic silicon compounds, such as
trichloromethylsilane.
The invention also provides a process for the production of
the silanised, structurally modified, pyrogenically
produced silicas according to the invention, which is
characterised in that pyrogenically produced silica is
treated with dimethyldichiorosilane and/or
monomethyltrichlorosilane by a known method, the
dimethylsilyl and/or monomethylsilyl groups being fixed on
the surface of the pyrogenic silica, and is then
structurally modified and optionally post-ground. The
silicas according to the invention have a tamped density of
280 g/1 or less.
In one embodiment of the invention a tempering. can take
place after the structural modification and/or post..-
grinding.
The silicas according to the invention can be produced e.g.
as follows:
The silicas, which can be produced as described in DE 1 163
784, are then structurally modified by mechanical action
and possibly post-ground in a mill. A tempering can
possibly take place after the structural modification
and/or post-grinding.,
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2a
The structural modification can take place e.g. with a ball
mill or a continuously operating ball mill. The post-
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grinding can take place e.g. using an air-jet mill or pin
mill. The tempering can take place batchwise, e.g. in a
drying cupboard, or continuously, e.g. in a fluidised bed.
The tempering can take place under protective gas, e.g.
nitrogen.
The silicas according to the invention can be incorporated
into lacquers, as a result of which these lacquers have
increased scratch resistance.
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Examples
Production and physico-chemical properties of the silicas
Production of the comparative silicas:
The production of the comparative silicas 1, 2 and 3 takes
place as described in DE 1 163 784.
Production of the silicas according to the invention:
The silicas, which are produced as described in DE 1 163
784, are then structurally modified by mechanical action
and possibly post-ground in a mill. A tempering can
possibly take place after the structural modification
and/or post-grinding.
The structural modification can take place e.g. with a ball
mill or a continuously operating ball mill. The post-
grinding can take place e.g. using an air-jet mill or pin
mill. The tempering can take place batchwise, e.g. in a
drying cupboard, or continuously, e.g. in a fluidised bed.
The tempering can take place under protective gas, e.g.
nitrogen.
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Example 1:
For the investigation of the improvement in scratch
resistance, a conventional 2-component polyurethane lacquer
was used. The formulation of the lacquer and its
production, including application, are summarised below:
Formulation
Millbase Parts
by wt.
Acrylic copolymer, mod. with synthetic fatty
acids, 60% solution 43.4
Butyl acetate 98% 17.8
Xylene 3.9
AEROSIL 5.0
70.7
Lacquer make-up
Xylene 11.3
Ethoxypropyl acetate 3.4
Butyl glycol acetate 1.6
Aliphatic polyisocyanate, approx. 75% in 1- 18.6
methoxypropyl-2-acetate/xylene 1:1
105.0
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Binder concentration: 40%
AEROSIL calculated on the basis of millbase (solids): 19.2%
AEROSIL calculated on the basis of lacquer (total): 5.0%
AEROSIL calculated on the basis of lacquer (solids): 12.5%
Production and application of the lacquers.
The binder is mixed with the solvents. Then, for the
purpose of predispersion, the AEROSIL is incorporated. into
this mixture with the high-speed mixer (disk 0 45 mm) and
predispersed for 5 min at 2000 rpm. The mixture is
dispersed in a laboratory pearl mill for 30 min at 2500 rpm
and 60% pump capacity using glass beads (0 approx. 1 mm).
The millbase is tested with a grindometer, 25 m, in
accordance with DIN ISO 1524. It must be smaller than
m.
The conversion of the millbase to lacquer takes place in
accordance with the formulation, the components being mixed
with a vane agitator at 2000 rpm. The hardener is
incorporated in the same way.
After adjusting the lacquers to spray viscosity in
accordance with DIN 53411, the lacquers are applied to
black lacquered metal sheets, e.g. DT 36 (fromQ-Panel) by
spray application (coat thickness about 40-50 m). After
spraying, the metal sheets are dried for 24 h at room.
temperature and then for 2 h in a drying oven at 70 C.
Scratch tests:
The metal sheets are abraded with a quartz/water slurry
(100 g water + 1 g Marlon A 350, 0.25% + 5 g SikrorMF500)
using an abrasion and washing-resistance tester (Erichsen,
brush with hog's bristles). The gloss before and 10 min
after the abrading is determined with a reflectometer (2.0
irradiation angle).
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The silicas 1 + 2 and 3 + 4 according to the invention can
be used in high concentrations without impairing the
appearance of the lacquer surface owing to their
substantially lower rheological efficiency compared with
5 comparative silicas 1 and 2. In addition, the silicas
according to the invention display a substantial
improvement in the scratch resistance of the lacquer
surface.
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Example 2
In this example the influence of the structural
modification was investigated on the basis of a high solids
2-component PU clear lacquer. The formulation of the
lacquer and its production, including application and
testing, are summarised below:
Formulation
Millbase Parts by wt.
Acrylic copolymer, mod. with synthetic
fatty acids,
70% in n-butyl acetate 61.0
Butyl acetate 98% 7.3
Methoxypropyl acetate 1.7
SolvessoM100 2.0
Xylene 2.0
BaysilonMOL 17, 10% in xylene (silicone
oil)
0.7
AEROSIL
5.0
E 79.7
Lacquer make-up (hardener)
Aliphatic polyisocyanate, 90% in n-
butyl acetate 22.3
Butyl acetate 98% 2.0
Solvesso 100 1.0
105.0
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Binder concentration: 62.8%
Aerosil calculated on the basis of millbase (solids):11.7%
Aerosil calculated on the basis of lacquer (total): 5.0%
Aerosil calculated on the basis of lacquer (solids): 8.0%
Production and application of the lacquers
The binder is mixed with the solvents. Then, for the
purpose of predispersion, the AEROSIL is incorporated into
this mixture with the high-speed mixer (disk 0 45 mm) and
predispersed for 5 min at 2000 rpm. The mixture is
dispersed in a laboratory pearl mill for 30 min at 25.00 rpm
and 60% pump capacity using glass beads (0 approx. 1 mm).
The millbase is tested with a grindometer, 25 m, in
accordance with DIN ISO 1524. It must be smaller than
10 m.
The conversion of the millbase to lacquer takes place in
accordance with the formulation, the components being mixed
with a vane agitator at 2000 rpm. The hardener is
incorporated in the same way.
After adjusting the lacquers to spray viscosity in
accordance with DIN 53411, the lacquers are applied to
black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by
spray application (coat thickness about 40-50 m). After
spraying, the metal sheets are dried for 24 h at room
temperature and then for 2 h in a drying oven at 70 C.
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Scratch tests:
The metal sheets are abraded with a quartz/water slurry
(100 g water + 1 g Marlon A 350, 0.25% + 5 g Sikron F500)
using an abrasion and washing resistance tester (Erichsen,
= 5 brush with hog's bristles). The gloss before and 10 min
after the abrading is determined with a reflectometer (200
irradiation angle).
Table 4: Summary of the properties of the liquid lacquers
relevant in terms of lacquer technology, and of the applied
10' and dried films.
Coarparative Silica Silica Reference
silica 2 3 4.
Grindaneter value [ m] < 10 < 10 < 10 /
Viscosity (millbase) [mPas]
6 rpm 6200 1500 541 140
60 rpm 2100 900 559 195
Viscosity (lacquer + hardener)
[mPas)
6 rpm 3821 1041 491 167
60 rpm 1320 666 446' 195
Flay marked
OR
orange-peel
20 reflectometer value before 81.0 83.5 82.8 88.0
scratching
Haze 25 5 6 2
40 strokes with Sikrcxi F 500
residual gloss [%3 94.3 93.4 82.0
The silicas 3 + 4 according to the invention can be used in
high concentrations without impairing the appearance of the
lacauer surface owing to their substantially lower
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rheological efficiency compared with comparative silica 2.
In addition, the silicas according to the invention display
a substantial improvement in the scratch resistance of the
lacquer surface.
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Example 3
Direct comparison of the silicas according to the invention
with a scratch-resistant lacquer according to DE 198 11 790
Al, in which AEROSIL R 972 is used to improve the scratch
5 resistance.
Prior art Silicas 2)
according to the
invention
Mi1ibase
Desmopher?"A 2009/1 190.2
Methoxypropyl acetate :
3.8
Solvesso 100 1:1
AEROSIL 23.0
E
J 250.0
Lacquer make-up
Desmophen A YEP4-55A, contains 96.0 -
AEROSIL R 972
Milibase - 48.9
DesmophenM2009/1- - 24.9
OL 17, 10% in MPA - -
Modaflow 1% in MPA - -
MPA : Solvesso 100 1:1 11.6 33.8
Butyl glycol acetate 10.5 10.5
ByketolTMOK 7.5 7.5
TM
Byk 141 0.8 0.8
Hardener addition
DesmodurMN 3390 23.6 23.6
E 150.0 150.0
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Production and application of the lacquers
1) Comparative silica 1 is incorporated into the binder
in accordance with DE 198 11 790 Al using a jet
disperser.
2) The binder is mixed with the solvents. Then, for the
purpose of predispersion, the AEROSIL is incorporated
into this mixture with the high-speed mixer (disk 0
45 mm) and predispersed for 5 min at 2000 rpm. The
mixture is dispersed in a laboratory pearl mill for
30 min at 2500 rpm and 60% pump capacity using glass
beads (0 approx. 1 mm). The millbase is tested with a
grindometer, 25 m, according to DIN ISO 1524. It must
be smaller than 10 m.
The conversion to lacquer of the millbases corresponding to
.1) or 2) takes place in accordance with the formulation,
the components being mixed at 2000 rpm with a vane
agitator. The hardener is incorporated in the same way.
After adjusting the lacquers to spray viscosity in
accordance with DIN 53411, the lacquers are applied to
black lacquered metal sheets, e.g. DT 36 (from Q-Panel), by
spray application (coat thickness about 40-50 m). After
spraying, the metal sheets are dried for 24 h at room
temperature and then for 2 h in a drying oven at 70 C.
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Scratch tests:
The metal sheets are abraded with a quartz/water. slurry
(100 g water + 1 g Marlon- A 350, 0.25% + 5 g SikronMF 500)
using an abrasion and washing resistance tester (Erichsen,
brush with hog's-bristles). The gloss before and 10 min
after the abrading is determined with a reflectometer (200
irradiation angle).
Table 5: Summary of the properties of the liquid lacquers
relevant in terms of lacquer technology, and of the applied
and dried films.
Prior art silica 1 Silica 4 Reference
Grindcoeter value [pmt] < 10 < 10 < 10 /
Viscosity (millbase)
[mPas]
6 rpm 58 30 26 30
60 rpm 48 43 33 40
wave scan
long wave 4.8 1.2 1.1 1.4
short wave 6.5 3.0 3.1 4.7
reflectceneter value 89.0 90.2 89.16 90.8
before scratching
Haze before scratching 4 4 3 4
40 strokes with Sikron F 500
Residua] gloss [%] 78.3 85.9 86.2 55.3
It is shown that a substantially better improvement in the
residual gloss is achieved after a scratch stressing of the
15 lacquer surface by using the silicas according to the
invention than with the prior art. In addition, owing to
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their low rheological efficiency, the silicas according to
the invention do not cause an orange-peel effect.
